Thermostat



(No Model.) W, JOHNSON.

THERMDSTAT.

No. 557,272. Patented Mar. 31, 1896.

UNITED STATES.

PATENT OFFICE.

\VARREN S. JOHNSON, OF MILIVAUKEE, WVISCONSIN.

TH ERMOSTAT.

SPECIFICATION forming part of Letters Patent No. 557,272, dated March31, 1896.

Application filed March 24, 1894. Serial No. 504,930. (No model.)

the same, reference being had to the accompanying drawings, and to theletters of reference marked thereon, which form a part of thisspecification.

My invention relates to that class of thermostats which are designed toautomatically control electric circuits and to be operated by change oftemperature. Its main objects are to facilitate the adjustment of thecontacts and generally to improve the construction and operation ofinstruments of this class.

It consists of certain novel features in the construction andarrangement of component parts of the device, hereinafter particularlydescribed, and pointed out in the claims.

In the accompanying drawings like letters designate the same parts inthe several figures.

Figure l is a front elevation of a thermostat, the cover being removedand a portion of the scale broken away. Fig. 2 is a vertical section ofthe complete thermostat, including the cover, 011 the line 2 2, Fig. 1;and Fig. 3 is a perspective view, on an enlarged scale, of thecontact-piece with which the expansion-strip is provided.

A designates the base, which is made of any suitable metal and isprovided with binding screws a and a a for the attachment of the wiresof the electric circuits in which the thermostat is to be placed.

1) h are platinum-pointed contact-screws adjustably held with theirpoints opposite each other in posts B B pivoted in the metal base A andinsulated therefrom, as shown in Fig. 2. They are electrically connectedwith the binding-screws a a" by metallic angle-plates h I) mounted uponsaid posts and with them insulated from the base.

0 is a lever which is fulcrumed at one end adjacent to thecontact-screws Z) Z) upon a pin 0 secured in the base and is forkedatits other and free end. D is a cam or eccentric accurately fittedbetween the arms of the forked end of said lever and provided with aspindle d, which is journaled in the base and formed at its front endwith a key-head d, which is exposed through an opening formed in thecover, as shown in Fi 2. The base is formed on opposite sides of saidlever with ears 6 e, in which are threaded, in line with each other,screws E E constituting adjustable stops for limiting the movement ofsaid lever in both directions or lockin g it in any desired position.

F is an expansion-strip composed of two different metals or materialshaving different coefficients of expansion. compactness it is preferablycoiled into a flat spiral, as shown in Fig. 1. It is inserted at one endin a slotted post f pivotally secured in the lever C, and is provided atits opposite free end between the contact-screws b b with acontact-piece consisting of a thin plate g, of platinum or othersuitable non-corrosive conducting material, folded into and held betweenthe folds of a metal strip G, and exposed on both sides through anopening made through both folds of said strip, as shown in Fig. 3. Bythis means a single piece of platinum is made to operate as acontact-piece in connection with both of the contact-screws b b, asaving of expensive material is effected, the construction of the deviceis simplied and its operation rendered certain and reliable by avoidingthe use of solder, the lead in which attacks the platinum.

By means of the post i, which is made to turn hard in the lever O, thecontact-piece g, which is carried by the free end of theexpansion-strip, may be readily ad j u.s ted approxi mately to itsproper position/"between the contact-screws b b and relative to saidlever, the exact permanent adjustment of the thermostat being made byturning the contact-screws b b in or out of the posts B B in which theyare threaded.

II is a graduated scale attached to the base over the expansion-stripand graduated to design ate the degrees of temperature at which thecontact-piece of the expansion-strip is adj usted and set to engage withone of the con tact-screws Z).

I is an index-hand mounted upon the spindle (Z of cam I) and projectingat its free end over or into close proximity with said scale, so as toindicate thereon the degree of temperature at which the instrument isset to close or open an electric circuit.

K designates the cover of the instrument,

For the sake of constructed to inclose and prevent ready or unauthorizedaccess to the electrical connections, contacts, and adjusting deviceshereinloefore mentioned. It is provided with a thermometer 7t in theusual manner for the purpose of verifying the operation of thethermostat, and has a glass or mica closed opening 79, through which thegraduated portion of the scale and the adjacent end of the index-handare exposed to view.

It will be observed that the movable contact-piece g, carried by thefree end of the expansion-strip, is located close to the fulcrum oflever C, while the cam D, by means of which the thermostat is adjustedto close or open a circuit at different degrees of temperature, isplaced at a much greater distance from said fulcrum. By this arrangementa considerable movement of the cam is caused to produce a still greatermovement of the free end of the index-hand over the scale and but acomparatively slight movement of said contact-piece, which can thus bereadily and accurately set to close or open the circuit at any desireddegree of temperature or within very narrow limits of variation.

I do not wish to be understood as limiting myself to the spiral form ofthe expansionstrip herein shown and described, as my improvements areapplicable to a straight or other forms as well. In short,variouschanges in the minor details of construction and arrangement of partsmay be made within the intended scope of my invention.

I claim 1. In a thermostat the combination with a suitable base providedwith opposite contactpoints, of a lever fulcrumed to said base, anexpansion-strip attached at one end to said lever at a distance from itsfulcrum and having a contact-piece at its free end between said pointsand close to the fulcrum of said lever and means of turning said lever,engaging it at a greater distance from its fulcrum than the contacts,substantially as and for the purposes set forth.

2. In a thermostat the combination with a suitable base provided withopgosite contactpoints, of a forked lever fulcrumed to said base, anexpansion-strip attached at one end to said lever and having at its freeend a contact-piece between said points and a cam or eccentric pivotedto said base and engaging the fork of said lever, substantially as andfor the purposes set forth.

3. In a thermostat the combination with a suitable base provided withopposite contactpoints, a lever f ulcrumed to said base, anexpansion-strip attached at one end to said lever at a distance from itsfulcrum and provided at its free end with a contact-piece between saidpoints, and close to the fulcrum of said lever, a cam or eccentricarranged to turn said lever in either direction, and engaging it at agreater distance from its fulcrum than the contacts, an index connectedwith said cam and a graduated scale in proximity therewith to indicatethe temperature at which the instrument is set to close or open anelectric circuit, substantially as and for the purposes set forth.

4. In a thermostat the combination with a suitable base provided with acover and with opposite contact-points, a lever fulcrumed to said base,an expansion-strip attached at one end to said lever and provided at itsfree end with a contact-piece between said points, a cam or eccentricpivoted to said base in engagement with said lever and having a stemprovided with a key-head exposed through an opening in the cover, agraduated scale and.

an index mounted upon the stem of said cam or eccentric and projectinginto proximity with the scale so as to indicate thereon the degree oftemperature at which the instrument is set to close or open an electriccircuit, substantially as and for the purposes set forth.

5. In a thermostat, the combination with a suitable base provided withopposing contactpoints, of a lever fulcrumed to said base so as to bemoved in the direction of a line connecting said points, anexpansion-strip pivotally attached at one end to said lever and providedat its free end with a contact-piece between said points, saidexpansion-strip being coiled or bent so as to shorten the distancebetween its contact-piece and its attachment to said lever, and means ofturning said le ver, engaging it at a greater distance from its fulcrumthan the distance of said fulcrum from the contact-piece of theexpansion-strip, substantially as and for the purposes set forth.

6. In a thermostat, the combination with a suitable base provided withopposing contactpoints, of a lever fulcrumed to said base, adjustablestops on opposite sides of said lever, an expansion-strip attached atone end to said lever and provided at its free end with a contact-piecebetween said points, said expansion-strip being coiled or bent so as toshorten the distance between its contact-piece and its attachment tosaid lever, and means of turning said lever, ei'igaging it at a greaterdistance from its fulcrum than the distance of said fulcrum from thecontact-piece of the expansion-strip, substantially as and for thepurposes set forth.

7. In a thermostat the combination of two opposite contact-points and anexpansionstrip provided between said points with a contact-piececonsisting of a plate of non-corrosive material folded into and held bya metal strip and exposed on each side through an opening made in thefolds of said strip, substantially as and for the purposes set forth.

In testimony that I claim the foregoing as my own' I affix my signaturein presence of two witnesses.

WARREN S. JOHNSON. lVitnesses:

E. B. I'IENIKA, CHAs. L. Goss.

